The invention relates to a motor vehicle rear axle assembly of the twist-beam axle type, comprising a longitudinal control arm 2 of a high flexural strength and torsional stiffness which carries a wheel carrier for a wheel, and a transverse strut 3 which is resistant to bending but resilient relative to torsional stress and which comprises a profiled cross-section changing the position of the shear center. The invention also relates to a method of producing said motor vehicle rear axle control arm assembly.
Motor vehicle rear axles of the aforementioned type are known from DE 43 30 192 A1 wherein a transverse strut having a U-profile cross-section is aligned and fitted in such a way that the upwardly extending angular U-profile raises the potential torsional axis of the transverse strut and achieves a correspondingly high shear center. The purpose of using such a U-profile is to achieve a method of construction which is uncomplicated from the point of view of welding technology and a good natural steering behavior due to only little or no oversteering tendencies. The prior art U-profile is bent out of metal plate with a uniform wall thickness. In the regions of transition to the longitudinal control arms, the legs of the U-profile are welded together to form a rigid box profile, with the two ends of the transverse strut being inserted into laterally open longitudinal control arms and connected to upper and lower plate metal dishes.
The U-profile of the transverse strut as described in DE 43 30 192 A1 is not uniformly aligned along the entire length of the transverse strut, as has previously been the case, but in the region between the two longitudinal control arms it is twisted around the longitudinal axis of the transverse strut, relative to the transverse strut ends welded to the longitudinal control arms, the twisting being such that in the central portion of the transverse strut, the axis of symmetry of the U-profile assumes a different inclination relative to the longitudinal extension of the longitudinal control arm and the road surface plane than in the end portions welded to the wall portions. Such twisting achieves the initially mentioned displacement of the hypothetical torsional axis and shear center within a narrow range illustrated by the axes I and II in FIG. 1 of DE 43 30 192 A1.
For a large number of applications, the possibility of a limited displacement of the shear center according to DE 43 30 192 A1 is not adequate. Furthermore, the wall of the U-profile must be thin, for reasons of weight, the permissible load values, especially in the case of cyclic loads, have to be kept very low for a transverse strut produced in the conventional way, because the twisted arrangement of the transverse strut ends may lead to a great deal of deformation and, in the case of excessive loads, even to cracks in the surfaces of the transverse struts, thus increasing the risk of fracture of the motor vehicle rear axle.
With reference to a motor vehicle rear axle of the initially mentioned type it is therefore the object of the invention to achieve a high degree of variability in arranging the torsional axis and shear center and thus a largely independent possibility of creating the natural steering behavior and, at the same time, to increase the permissible load values, especially in the case of cyclic loads, while achieving advantageous weight/wall thickness ratios.